<!DOCTYPE html><html><head>
   <title>Bootstrap 实例 - 警告框（Alert）插件</title>
   <link href="bootstrap.min.css" rel="stylesheet">
    <script src="jquery-3.3.1.min.js"></script>
   <script src="bootstrap.min.js"></script></head><body><div class="alert alert-warning">
   <a href="#" class="close" data-dismiss="alert">
      &times;   </a>
   <strong>警告！</strong>您的网络连接有问题。</div></body></html>